A gasket and seat system of the kind described above is for example shown in DE-A-42 01 535. The sealing according to this system will provide a gasket being flush with the interior surfaces of the pipes and it has some provisions for heat expansion.
Gasket and seat systems that provide gaskets flush-mounted with the interior surfaces of pipes are for example desired in the pharmaceutical and food industry. For instance, the ISO 2852 standard of 1993 defines stainless steel pipe couplings for the food industry, wherein a gasket is disclosed as a ring-shaped pipe coupling part intended to make a hygienic liquid-tight joint between the flanges of two clamp liners. This kind of sealing system is intended to prevent residue and bacteria from accumulating in pipe joints, especially e.g. in crevices of the sealing system. The pipes of these facilities are regularly cleaned by CIP (Cleaning In Place) and SIP (Sterilization In Place) with hot steam (140° C.) in order to kill bacteria that may be present in the pipes. This means that the gaskets must be able to handle heat expansion while remaining flush, or almost flush, with the interior surfaces of the pipes even during steam washing. If the gaskets project from the pipe interior, they can further induce turbulence in the pipes and this may be unwanted in some cases. The gasket disclosed in ISO 2852 does not have provisions against such expansion into the pipe interior caused by a difference in the expansion coefficients of the pipe material and the gasket material. Furthermore, the same problem applies to other types of joints than pipe couplings, having similar sealing purposes, for instance a heat exchanging system for heating a product inside a pipe. In this case different operating temperatures cause a different amount of expansion during operation. The sealing has to cope with these varying operating conditions without causing undesired crevices, as explained above.
With a gasket and seat system of the known kind, there is no provision for improving the sealing ability during periods with increased pressure in the pipes. The gasket inner portion is also rather large, which increases the risk of this portion expanding, due to increased heat, into the interior of the pipes. Since the gasket furthermore is symmetrical, machining is necessary in both parts of the coupling in order to form an appropriate seat. The same problems occur with known gasket and seat systems for similar couplings, e.g. in pump housings of food pumps.
Hence, there is a need for a more advantageous sealing system.